Acetyl cellulose and process of making the same.



. and a process of making the same.

. UNITED STATES PATENT OEEIoE.

e. LINDSAY,

0E nEwmx, NEW JERSEY, vllssnmon 'ro THE cELLULom COMPANY, A CORPORATION OF JERSEY.

AOETYL cEnLuLosEmn PROCESS or MAKING THE sum.

1,265,216. Io Drawing. Original application known that while acetyl cellulose is a desirable substance for replacing nitrocellulose in many applications, the special difiiculties connected with its manufacture have, in large part, prevented its adoption for practical purposes. The acetylation of cel-, luloseis so sensitive to the influence of acetylizing mixtures and physical conditions that up to the present time it has been hard to roduce a definite and uniform product.

he principal diflicult has been the production of acetyl cellu ose having a conserved strength of fiber and such a definite solubility as would fit it for use with oer-- tain solvents, or for application to particular purposes in the arts. 4 Previous to my invention the products ofthe various processes proposed have been strictly circumscribed because of their defects or practical limitations. For example, the acetyl cellulose would be in one case-limited to the amorphous form and a definite solubility. .In another case the form would be similarly limited, but the solubility would have a wider ran e. In another case the result would be a fi rous acetyl cellulose, but weak and brittle. In still another case there would be a better conservation of the fibrous form, but a limited solubility or degree of acet lization.

T e varying steps of manufacture are, therefore, of extraordinary importance, as they so strongly affect the final character .of' the'acetyl ce lulose. The process which I propose produces acetyl cellulose havin new characteristics. In practice I procee as follows: 4 Y

Cellulose, preferably ahigh grade bleached cotton, is given a h with acetic acid of a out 75% to 98% until reliminary treatment acetic acid be replaced by alcohol, either- Speciflcation of Letters Patent. Patented May 1918, filed Apri18, 1911, Serial no. 619,685. Divided and this'application fled July 11, 1914. Serial n. 550,431.

I the cotton is thoroughly impregnated. The 'mixture of cotton and acetic acid is then introduced into the acetylizin mixture consisting of acetic anhydrid, su furic acid and 1 benzene, the temperature being from 50 to 60 F., and under certain circumstances 80 F. The temperature of the reaction mixture gradually rises and is then usually maintained at from 70 to 80 F;, until the reaction is completed. This; takes from 24 to. 30. hours, depending upon the rate of acetylization. By this means I- obtain fibrous acetyl cellulose, having a wide range of solubility, such solubilit being varied according to the minor con itions of operating hereinafter described.

To some extent I control the solubility. of mfy plroduct, either by changing the strength 0 t e acetic acid used in the preliminary bath, or by varying the amountv of acid used in proportion to the fiber. For example, when using about 200 parts of acid'to 100 parts of fiber, I employ acetic acid varying. from about 75% to 98%. When usin an 85% acetic acid as a constant strength employ, say, from about 70 to 250 parts to each 100 parts of the'fiber. By this means.v

I can produce an acetyl cellulose soluble in a mixture of chloroform and alcohol, but

incompletely soluble in chloroform alone; or

. a variety which is quite viscous in acetone,

'or one which produces more fluid solutions.

Some of my acetyl cellulose is freelysoluble in acetylene tetrachlorid, while some requires the addition of alcohol before the acetylene tetrachlorid will make a-complete solution.

I also vary the solubility in different solvents by changes in the proportion of. S111- furic acid in the acetylizing mixture, and also by means of time of contact and the temperature, as is generally understood.

So far as I can ascertain, the preliminary treatment i above described produces no chemical effect upon the fiber, but simply puts it into a better condition for the subsequent reaction. In'other words, when the fiber enters the acetylizing inixture it is still ordinary cellulose.

I have also discovered certain equivalents of the acetic acid for my preliminarytreatment. For example, if the water in. the

ethyl or methyl, the effect is apparently the same. Or in place of the acetic acid I can use a mixture of benzene and ethyl or methyl alcohol, in which case the benzene will represent the pure acetic acid, and the alcohol will represent the water. Or the acetic acid can be replaced by ethyl acetate of similar strength; or I may use, say, a mixture of readily react with acetic anhydrid and sulfuric acid, but tends to regulate or prolong the initial reaction. Water alone would not be such a liquid, because it would increase the violence of the first attack.

In order to still. further instruct the operator, I give the following proportions and conditions as a specific example of my improved process. Upon 100 parts by weight of pure cotton rovingsis poured 200 parts of 90% acetic acid. After the acid has become uniformly spread throughout the mass, the mixture is introduced into a bath consisting of 600 parts of acetic anhydrid, 25 parts of 96% sulfuric acid, and M00 parts of benzene, at a temperature of about 50 F. The acetylation is then allowed to proceed at a temperatureof about 70 F. for 24: hours, at the end of which time, if the conditions given be .properly observed, a test portion should. be soluble in a mixture 'of acetylene tetrachlorid and alcohol, di-

chlorhydrin, epichlorhydrin, or .nitroben The excess of the reaction mixture is then i removed by any suitable means; for example, by 'whizz'ing or by pressing. The acetyl cellulose'is then immersed for one hour in a hot solution of-calcium nitrate (consisting.

of about onepound to the gallon), after which it is thoroughly washed, preferably in hot and then in cold water, and then dried.

The object of this treatment with cal cium nitrate is to remove any free sulfuric acid adhering to the fiber, and also to neutralize any sulfonic acid ester that might accompany the formation of the acetyl cellulose.

The acetyl cellulose produced in this par ticular instance is, in appearance, quite similar to nitrated cotton in which the strength of the fiber has beenretained. That.-is, it

, is harsh to the touch and practicallyas strong as the origmal cotton fiber. It can be dissolved in a mixture of acetylene tetra chlorid and alcohol or in a mixture of chloroform and alcohol to form a fiowable solution suitable for the manufacture of thin sheets, or, after being rendered plastic by the addition of the solvents mentioned, it can be manipulated so as to produce other forms.

The acetyl cellulose made by the formula just described has an increase from the cellulose tothe final product of about 65%. In general, the increase of weight bears some relation to variations in solubility, and depends upon the character of the first solution and the conditions of acetylization. In practice the increase obtained by m process has varied from 50% to 80% and even higher. r

As to this influence of the acetylizing mixture and the conditions of acetylization, I might add that increase in weight is produced by prolonged reaction. The temperature will also .have its effect. But in all cases the, influence of the acetic acid into which the cotton is first immersed is greater than the efiect of the acetylizing mixture, or time and temperature. I therefore call the operators attention especially to the importance of this first step in my process.

The proportion of sulfuric acid in the acetylizing mixture is also of some importance in controlling the variety of acetyl cellulose produced. While I prefer to use cellulose in the form of cotton, it is understood, of course, that I can use other vegetable fibers suitably prepared,

The acetyl cellulose made by my process j does not consist of any one variety or degree of acetylation. his not, for example, di-, or trior tetraacetyl cellulose. very mixture or combination is of great practical importance, as furnishing products specially suitable for industrial applications.

Having thus described my invention, I declare that what I ,claim as new and desire to secure by Letters Patent is 1. The process of producing acetyl cellulose which consistsin treating cellulose with acetic acid and alcohol, and then subjecting the impregnated cellulose to an acetylizin mixture comprising acetic anhydrid an benzene.

2. The process of producing acetyl cellulose which consists in treating cellulose with acetic" acid and alcohol and subjecting the mpregnated cellulose to an acetylizing mixture.

3. The process of producing acetyl cellulose whichconsists .in treating cellulose with treated cellulose to an acetylizing mixture. 4. The process of producing acetyl cellu lose which consists in treating cellulose with And this.

* a bath containing j alcohol and a diluent therefor which does not substantially alter the cellulose as such, and then subjecting the treated cellulose to an acetylizing mixture, said preliminary bath being miscible with the acetylizingmixture.

-5. The process of producing acetyl cellulose which consists in treatm with a bath containing alcohol an a diluent therefor which does not substantially -alter the cellulose assuch and thereafter subjecting the treated cellulose to an acetylizin mixture of acetic anhydrid, sulfuric aci and benzene.

6; In the process of producing acetyl cel-' lulose from cellulose, the preliminary ste which consists-in treatin the cellulose wit a bath comprising alco 01 and a diluent therefor which does not'substantially alter the cellulose as such, and which prepares the cellulose to induce acetylization thereof cellulose and protects it against too rapid acetyliza-- tion,

7. The process of producing'aoetyl cellulose which consists in treat ng cellulose with a preliminary bath comprising alcohol and a diluent therefor, which, without itself structure-unaltered, and being solub e in acetylene tetrachlorid. V

In testimon whereof I afiix my signature, in presence 0 two witnesses.

WILLIAM G. LINDSAY. Witnesses: I

C. V. Enwums, C. GALvIoN. 

